import java.util.Scanner;

public class Main1003 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int a = 0;
        if (n % 2 == 1) {
            for (int i = 1; i <= n; i+=2) {
                a = a + i;
            }
            System.out.println(a);
        }
    }
}
